1) eotriceratops (15t) vs 6 utahraptors (600kg): Eotriceratops was a larger version of Triceratops, and was armed with 2 long sharp brow horns used (allegedly) to impale adversaries. It also had a smaller nose horn and a large neck frill (that afforded it protection from attacks to the neck & other anterior areas). Utahraptors were slender, agile, theropods with good leaping ability. They were believed to occasionally hunt in groups, and were armed with decent bites, clawed forelimbs (to grab & hold), & clawed hindlimbs (to kick & slash). Eotriceratops is the more powerful participant in this matchup by far, but 6 Utahraptors attacking en masse can be problematic for a single opponent (even if much larger & well-armed). Eotriceratops can easily kill a Utahraptor by stabbing, trampling, or even biting one, but effectively repelling multiple ones (especially ones clinging & attacking on its posterior half) will be difficult. It will take a while to seriously injure the ceratopsian, and the Utahraptor's numbers will likely be reduced before too much time has passed. Eotriceratops' ability to fight well, along with its massive size advantage, should give it the assets needed to survive this encounter & prevail. Eotriceratops wins.

2) eotriceratops (15t) vs 3 albertosauruses (2.5t): Albertosaurus had large jaws, sharp teeth, and decent speed for its size. However, 3 of them would be at a disadvantage against a ceratopsian 6 times their weight (Albertosaurus' standing height would only be slightly more than the shoulder height of this Eotriceratops). Eotriceratops would be able to knock the smaller theropods around, finishing them with its crushing weight or impaling horns. Many bites would be needed by the Albertosauruses to make a serious dent in Eotriceratops, and the time to deliver them simply won't be there. Eotriceratops wins.

3) eotriceratops (15t) vs barosaurus (25t): Barosaurus was a slenderly-built sauropod, and likely used its long tail to strike attackers. Eotriceratops was armed with 2 long horns extending from it forehead area. Despite weighing less, the weaponry of Eotriceratops was more formidable, and would be more combat-effective in this matchup. Barosaurus likely chose to flee predators as its initial reaction to a threat, but the ceratopsian likely stood its ground in encounters with theropods. Eotriceratops wins.

4) eotriceratops (15t) vs 2 allosauruses (4.5t): The 2 Allosauruses, when standing upright, would only be a little bit taller than the shoulder height of a 15-ton Eotriceratops. Allosauruses were fearsome hunters with bladelike teeth designed to remove large chunks of flesh (and may have hunted in groups). At only 30% of the herbivore's weight, however, the Allosauruses would have had trouble delivering bites without getting trampled or gored by this huge ceratopsian. The difference in power among these adversaries would be significant at these sizes. Eotriceratops wins.

4b) eotriceratops (15t) vs 2 indian elephants (5t): Elephants are the largest modern land animal, and are armed with great weights and sharp tusks. However, against an Eotriceratops weighing 3 times as much, they will pale in comparison. The weapons of Eotriceratops can be utilized much more effectively, and its large size will give it the ability to bully the smaller pachyderms around quite easily. Eotriceratops wins.

5) triceratops (10.5t) vs T-rex (10t): This is a classic matchup, and it likely occurred from time-to-time. Triceratops was armed with 2 long sharp brow horns used (allegedly) to impale adversaries. It also had a smaller nose horn and a large neck frill (that afforded it protection from attacks to the neck & other anterior areas). Tyrannosaurus has long been referred to as the "king of dinosaurs", and was believed to be the largest land predator ever for many years (until the discovery of such giants as Carcharodontosaurus & Giganotosaurus). Tyrannosaurus was an impressive carnivore, with a head over 1 1/2 meters long & teeth over 15cm in length. The key for Triceratops in this battle would be to keep Tyrannosaurus in front of it so that its 2 longest horns would be ready to stab the theropod as it approached. Tyrannosaurus will need to circle around to bite the unprotected back & flanks of Triceratops while avoiding the dangerous horns. Tyrannosaurus was probably well-practiced at getting around the defenses of various prey items, but Triceratops was likely experienced at repelling attacking theropods. Tyrannosaurus would have an increased chance to prevail by utilizing an ambush, but will be seriously challenged in a face-to-face encounter. Even at exact parity I favor the Triceratops, but both dinosaurs have decent chances to come out on top. Edge to Triceratops.

6) triceratops (10.5t) vs diplodocus (15t): This is similar to the Eotriceratops vs Barosaurus matchup, but the size difference isn't as significant (here the ceratopsian is 70% of the sauropod's weight; in the other matchup it is 60%). Triceratops is more battle-tested & better armed. Triceratops wins.

7) triceratops (10.5t) vs songhua river mammoth (18t): The Songhua river mammoth is now believed to actually be a Steppe mammoth, and didn't likely reach the sizes originally assigned to it. The Songhua river mammoth was a resembled an elephant, but was much larger & had longer tusks (and smaller ears). Its huge tusks (sometimes 5 meters in length) were curved upwards, and therefore weren't positioned for effective stabbing. However, the force of their impact would have cause concussive injuries quite easily (especially against a smaller opponent). Triceratops had better overall weaponry (long brown horns, protective neck frill), and was accustomed to dealing with predatory adversaries (like Tyrannosaurus) close to its own size. A triceratops would easily defeat a mammoth at parity, but here it's giving up a lot of weight. The triceratops could get injured trying to charge if it is met forcefully by the charge of a mammoth weighing over 70% more than it does. Reasonably close fight; edge to Songhua river mammoth.

7b) triceratops (10.5t) vs 2 black rhinos (2.5t): Black rhinos are considered to be the most aggressive of all rhinos, and are armed with tank-like bodies and a long (over 1 meter) frontal horn. Triceratops has 2 long brow horns and a neck frill, and is practiced at taking on dangerous adversaries within its weight range. Triceratops would easily dispatch one of the smaller rhinos soon after initial contact, and then turn to defeat the other one. The rhinos don't have enough size to deal with a ceratopsian weighing over 4 times as much. Triceratops wins.

8) grizzly bear (650kg) vs smilodon populator (500kg): Grizzly bears are among the most aggressive of bears, and have large shoulder humps of muscle that enable them to deliver powerful swipes. Bears are durable, have great endurance, and formidable bites. Smilodon populators were powerful, muscular felids with the ability to wrestle prey items to the ground with their forelimbs and deliver a fatal bite with their long upper canines. They were capable of agile & explosive movements (not quite on par with today's big cats in that regard). The bear's larger size will give it an edge in the positioning battle once these 2 engage, and its better endurance will give it an increased advantage as time passes. Smilodons are more practiced than bears at taking down large opponents, but a bear has the assets (swiping/grabbing paws, supple body) to fight back better than most of Smilodon's prey targets. A Smilodon will be favored at parity, but here it's giving up a little bit too much weight. Edge to grizzly bear.

9) steppe buffalo (900kg) vs javan rhino (1200kg): The Javan rhinoceros is a strong, stout animal with a short horn on its nose. The Javan rhino is similar to the Indian rhino in that it bites. It isn't as formidable (pound-for-pound) as the white or black rhino, but it's still a tough adversary. The steppe bison was similar in appearance to a modern-day bison (muscular forequarters, short curved horns, etc.). A Javan rhino with this weight advantage will have an advantage in brute strength, and can use its horn as effectively as the buffalo could use its horns. Javan rhino wins.

10) steppe buffalo vs wild boar (at parity): The steppe bison was similar in appearance to a modern-day bison (muscular forequarters, short curved horns, etc.). It likely fought by using its head like a battering ram & hooking with its horns. Wild boars are nimble mammals with tough hides, sharp tusks, and fierce dispositions. A Steppe bison weighed about 5 times as much as a typical full-sized wild boar, so scaling up the pig will give it a decent mobility/speed advantage (and a similar shoulder height). The boar will be able to use its tusks in a swifter manner than the buffalo will be able to use its head/horns, and will be able to dish out more damage than it receives. Wild boar wins.

11) stegosaurus (6t) vs elasmotherium (6t): Stegosaurus was a herbivorous dinosaur with large plates along its back and a tail ending in 4 spikes (each almost a meter long) that made formidable weapons against attacking theropods (like Allosaurus). Elasmotherium was rhinoceros-like, but with a more robust build and a long, thick horn (not cone-like, but sword-like) protruding from its forehead that provided great reach & injury potential. Stegosaurus could injure Elasmotherium with a swing of its spiked tail, but a charge into the side of the dinosaur by the mammal would be more easily done, and a stab by the long horn could quickly end the battle. Elasmotherium wins.

12) megacerops vs elasmotherium (at parity): Megacerops (also called Brontotherium; formerly called Brontops), had a rhino-like build (similar to Elasmotherium) and a thick, forked horn that protruded from its nose. This horn was comparatively short & blunt compared to the long sword-like horn of Elasmotherium, and wasn't nearly as combat-effective. Elasmotherium wins.

12b) megacerops vs white rhino (maximum size): There are many varying estimates for the weight of Megacerops; some place it below the weight of a white rhino's max (4 tons, but 2.5 tons is a more typical top-end weight) and some place it as the same. Megacerops had a rhino-like build and a thick, forked horn that protruded from its nose. It had a greater shoulder height than a rhino of equal weight (longer legs). The white rhino has a long, sharp frontal horn that can be used effectively as an offensive weapon (and is more combat-effective than the relatively short & blunt horn of Megacerops). The white rhino has the edge at parity, and will likely win at a slightly lower weight. Edge to white rhino.

13) buffalo (900kg) vs 2 lionesses (160kg): Lionesses are great at teamwork, and can successfully collaborate to overpower large prey items. Lionesses have good weaponry (jaws & claws), and are quick, agile, athletic, and experienced at killing. Buffalo are rugged & strong, and are armed with dangerous hooves & horns to defend themselves with. These herbivores can make powerful movements & thrusts with their horns, and can easily kill an attacking lioness. Lionesses use their forepaws to gain control of their quarry's movements and bring them to the ground, but this action will be difficult for 2 of them against a buffalo weighing over 5 1/2 times as much as they do. It's not an impossibility, but the lionesses will be facing an uphill battle here. They will wisely wait for backup or target an easier meal. Buffalo wins.

14) pleistocene hippo (5t) vs 4 barbary lions (300kg): This hippo was similar to a modern-day hippo. A 5-ton hippo will be almost as tall at the shoulder as a white rhino. Hippos have huge, wide-opening jaws armed with massive canines & forward-pointing incisors, and very thick skin. The Barbary lions will have the typical big cat assets (speed, agility, athleticism, jaws & claws, killing know-how), and will have the mobility to avoid the hippo's offense as long as they are cautious. They will be able to jump on the hippo's back and begin gnawing & clawing in an attempt to subdue it, but this will take a very long time. Lions don't have a lot of endurance, and the 4 Barbary lions will likely break off their attack after they determine it's not worth their time to proceed. Theoretically the lions can prevail if they stick to their attack, but realistically they won't try. This is similar to 4 lionesses taking on a modern-day river hippo, and their success will be no greater. Edge to Pleistocene hippo.

15) megatherium (5t) vs 3 ceratosauruses (1400kg): Megatherium (giant ground sloth) was huge, standing over 6 meters (20ft) tall and weighing as much as an Asian elephant. Its hide consisted of small pieces of bone than formed an armor like chain mail, and protected it from injury. Megatherium also had large forelimbs armed with claws that could be used to deliver powerful swipes. Ceratosaurus had large jaws with sharp teeth, and strong hind legs for fast running. The bite of Ceratosaurus would have been effective on certain areas of Megatherium's body (head, limbs), but the much more powerful mammal would have knocked the smaller theropods around as they came into range. Despite its limited mobility, Megatherium would have gotten enough protection from its hide to be relatively safe while it swung its massive forelimbs in defense. Megatherium wins.

1) amphicyon ingens (850kg) vs grizzly bear (650kg): Amphicyon (bear dog) was a stocky carnivore with a build somewhere between an ursid (bear) and a canid (dog). It had very strong jaws set in a robust skull and solid, sturdy limbs. Grizzly bears are among the most aggressive of bears, and have large shoulder humps of muscle that enable them to deliver powerful swipes. Bears are durable, have great endurance, and formidable bites. The grizzly bear in this matchup will have better use of its forelimbs to control positioning, but the size advantage (and bigger bite) of Amphicyon will likely erase that advantage. Reasonably close fight at parity (edge to the bear), but the grizzly bear is giving up too much weight here. Amphicyon ingens wins.

2) amphicyon ingens (850kg) vs smilodon populator (500kg): Smilodon populators were powerful, muscular felids with the ability to wrestle prey items to the ground with their forelimbs and deliver a fatal bite with their long upper canines. They were capable of agile & explosive movements (not quite on par with today's big cats in that regard). Amphicyons had strong jaws that could crush bone, and Smilodon had a specialized bite that was most effective when a particular area (like the vulnerable neck) was targeted. Smilodon would win a fight at parity (paw usage & presence of claws would be key), but here it's giving up too much weight. Amphicyon ingens wins.

3) amphicyon ingens (850kg) vs 2 barbary lions (300kg): Lions occasionally work well in unison to overpower large prey items, but an Amphicyon of this size would be able to easily injure a lion with its strong bite. The task of controlling Amphicyon's movements with their forepaws while simultaneously avoiding its jaws would be quite challenging for the smaller lions, and the chances of one getting into position to deliver a finishing bite would be poor. From a size perspective, this would be like 2 clouded leopards trying to tackle a spotted hyena. The cats can pull it off, but they won't be favored. Amphicyon ingens wins.

Expertise

Questions regarding animal conflicts within realistic or unrealistic settings are welcome; my strength lies in medium-to-large species. Small animals (including birds of prey), prehistoric animals, sea creatures, and domestic dog breeds are usually within my scope, but to a lesser degree. I can't confidently answer hypothetical questions about human vs animal, arachnids, insects, or amphibians, but I am willing to field them nonetheless.

Experience

From a young age, I have been interested in animals. Starting with the original Mutual of Omaha's Wild Kingdom and World Book Encyclopedias, I have seen many animal shows and documentaries and have read multiple books on the subject. I have a solid understanding of the physiology of many animals and interspecies conflict in general.